1. Field of the Invention
This invention relates to a navigation system for a vehicle wherein a current driving position and a current driving direction of the vehicle are indicated on a display screen of a display unit making use of the global positioning system (GPS).
2. Description of the Prior Art
A conventional navigation system for a vehicle based on satellite navigation of the type mentioned normally involves position indication for indicating a current driving position of the vehicle in accordance with information received from a GPS receiver and heading indication for indicating a current driving direction of the vehicle.
In particular, a map around a point at which the vehicle currently drives is normally displayed on a display screen of a CRT (cathode ray tube) display unit located adjacent the driver's seat of the vehicle, and a suitable mark such as, for example, a round mark is indicated on the map to effect position indication while a small figure or graphic pattern of the vehicle is drawn, for example, at a right upper corner of the display screen to effect heading indication.
With such conventional navigation system for a vehicle, however, since a driving direction of the vehicle is calculated from information received from a GPS receiver, when the driving speed of the vehicle (hereinafter referred to merely as driving speed) is low such as, for example, 4 km/h to 5 km/h, the error in direction calculation is so great that a significant error may take place in heading indication, which will cause the driver to be bewildered or get lost.
A navigation system is also known wherein a direction to a destination is additionally indicated on the CRT screen. Referring to FIG. 8, there is shown an exemplary one of display screens of conventional navigation systems for a vehicle of the type just mentioned. The display screen 9a shown has a map 19 displayed thereon. A destination mark 21 in the form of a dot indicating a destination of the vehicle, a current position mark 22 in the form of a dot indicating a current position of the vehicle, a direction marker 23 in the form of a blank arrow mark indicating a direction to the destination 21 when the destination 21 is viewed from the current position 22, and a driving direction marker 24 in the form of a blank arrow mark indicating a direction in which the vehicle is currently driving or directed, are indicated on the map 19 displayed on the display screen 9a.
When the map 19, destination 21, current position 22, destination direction marker 23 and driving direction mark 24 are displayed on the display screen 9a in this manner, the driver can reach the destination 21 by driving the vehicle such that the driving direction marker 24 may coincide with the destination direction marker 23.
With such conventional navigation system for a vehicle as described above, as the vehicle drives, the orientation of the driving direction marker 24 is successively varied to various directions while the orientation of the destination direction marker 23 is also varied. Consequently, it cannot be discerned intuitively in what direction the destination 21 is positioned with respect to the driving direction of the vehicle. Accordingly, the navigation system is inferior in convenience in use in that point.